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<p>A generalized relational model which is capable of representing and manipulating disjunctive and maybe kinds of information is presented. A data structure, called M-table, is defined, and the information contained in the M-table is precisely stated. Redundant information in M-tables is characterized, and an operator to remove this redundant information is presented. The relational algebra is suitably generalized to deal with M-tables. Additional operators, R-projection and merge, are presented. Queries can be expressed as a combination of the various generalized relational algebraic operators. The M-table accurately models the two bounds on the external interpretation of a query. The sure component of an M-table corresponds to one of the bounds which is the set of objects which belong to the external interpretation of the query. The maybe component of an M-table corresponds to the other bound which is the set of objects for which the possibility of belonging to the external interpretation of the query cannot be ruled out.</p>
indefinite information; generalized relational model; maybe information; data structure; M-table; R-projection; merge; data structures; relational databases
K.-C. Liu, R. Sunderraman, "A Generalized Relational Model for Indefinite and Maybe Information", IEEE Transactions on Knowledge & Data Engineering, vol. 3, no. , pp. 65-77, March 1991, doi:10.1109/69.75890
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